Altered topological patterns of brain networks in remitted late-onset depression: a resting-state fMRI study

We aimed to investigate the topological organization of whole-brain networks in patients with remitted late-onset depression (rLOD) and to examine the relationship between topological aberrations and performances on neuropsychological tests.

A total of 33 patients with DSM-IV-diagnosed rLOD and 31 healthy control subjects underwent resting-state functional magnetic resonance imaging scans. The whole-brain functional networks were constructed by thresholding Pearson correlation matrices of 90 brain regions, and their topological properties (ie, small-worldness, network efficiency, and nodal efficiency) were analyzed using graph theory-based approaches. Nonparametric permutation tests were further used for group comparisons of topological metrics. The patients were recruited from January to December 2007.

Both the rLOD and control groups showed small-world architecture in the functional brain networks, suggesting a balance between functional segregation and integration. Importantly, the rLOD patients exhibited abnormal global topology in their functional brain networks (ie, increased shortest path length and decreased network efficiency) compared with the healthy controls, implying a less optimal topological organization in rLOD. Moreover, the rLOD patients showed decreased nodal efficiencies, predominantly in the frontal-striatal-occipital regions that are closely associated with the neuropathological changes in LOD. Intriguingly, we showed that the topological aberrations correlated with the neuropsychological performances in the rLOD patients.

These results demonstrate that the topological organization of functional brain networks is disrupted in rLOD and that this disruption may contribute to disturbance in cognitive function in rLOD patients.